The present invention relates to assuring the thickness of a sealant. More specifically, the invention relates to using ultrasonic techniques to determine the thickness of a sealant.
Submarine fiber optic communication systems carry a large majority of the information that is transmitted between the world""s continents. These fiber optic communication systems remain in-place on the bottom of the ocean under thousands of feet, and even miles, of water for years at a time. Due to the difficulties encountered when having to repair, replace, or generally service these systems, it is desirable that these systems be highly reliable.
Submarine fiber optic communication systems typically include repeaters that appear at regular intervals along the spans of undersea cables to amplify the optical signals traversing the constituent fibers. Other assemblies that may be found along a submarine communication system including branching units, which allow multiple cable stations to be served from a single cable. To protect the sensitive components and/or connections that are housed within these submerged assemblies, a rugged hermetically sealed structure must be employed.
FIG. 1 illustrates a cross-sectional view of a known submarine fiber optic communication device 10. Communication device 10 can be surrounded by seawater 12, and can be connected to other submarine fiber optic transmission devices (not shown) or to terminal units (not shown). Device 10 can be formed as a cylindrical container 14. Once the internal optical components (not shown) are installed within cylinder 14, an end cover 16 can be attached onto each of its longitudinal ends. Each transmission device end cover 16 can define a seal well 80 having an aperture that penetrates cover 16. Each seal well 80 can surround a seal assembly 100. An external communications cable 20 can connect to each seal assembly 100.
FIG. 2 provides a cross-sectional view of seal assembly 100, within which external communications cable 20 can be connected to internal communications cable 36. External communications cable 20 can contain an external secondary jacket 22 which can surround an external fiber shield 24 through which optical fibers 38 can pass. External guide tube 24 can be connected to tube 28, which can be connected to internal guide tube 34. Thus, a continual chamber 40 can be formed through which optical fibers 38 can pass from the outside to the inside of device 10 (not shown in FIG. 2). Internal guide tube 34 can be surrounded by internal secondary jacket 32.
Seal assembly 100 can have a circular cross-section, and can include an elongated annular plunger 110 having plunger front face 112, plunger rear face 114, and plunger circumferential face 116. Seal assembly 100 can also include an elongated annular disk 120 having disk front face 122, disk rear face 124, and disk circumferential face 126. Although plunger 110 and disk 120 can be coaxial, plunger 110 can have a larger outer diameter than disk 120.
Sealant 130 can be attached to, and formed simultaneously with, internal secondary jacket 34 and external secondary jacket 22. Sealant 130 can also be molded over disk front face 122 and disk rear face 124 of disk 120, as well as around circumference 126 of disk 120, to form encased disk 140. Encased disk 140 can be coaxial with disk 120, and can define sealant front face 142, sealant rear face 144, and sealant circumferential face 146. Plunger front face 112 can be attached to sealant rear face 144, such that plunger 110 and encased disk 140 are coaxial. A sufficient amount of sealant 130 can be removed from the circumference of encased disk 140 so that sealant circumferential face is flush with plunger circumferential face.
Plunger 110 and disk 120 can be constructed of any material that can withstand the loads anticipated to be imparted thereon. Sealant 130 can be constructed of polyethylene. Alternatively, sealant 130 can be constructed of any dielectric material that can sufficiently deform under preselected pressures to form a seawater seal.
FIG. 3 shows a cross-sectional view of seal assembly 100 installed in seal well 80. Seal assembly 100 can be installed in seal well 80 with rear face 114 of plunger 110 facing seaward. Seal well 80 can define well base 82 across its annular bottom, and well surface 84 along its inner circumference. Sealant front face 142 can contact well base 82 to form primary seal 150. Sealant circumferential face 146 can contact well surface 84 to form secondary seal 160.
Primary seal 150 and secondary seal 160 can be formed by applying pressure to sealant 130. Although this pressure can be supplied by the hydrostatic pressure of seawater 12 bearing against the rear face of plunger 110, it can be desirable to create at least primary seal 150 during the manufacture of device 10. The load necessary to establish at least primary seal 150 can be provided by the force of spring 170 bearing upon plunger rear face 114. Spring 170 can be contained in seal well 80 by retaining ring 174, which can ride in a retaining ring groove 86 that is cut in seal well 80. The pressure of spring 170 can create an axial force against plunger rear face 114. From plunger 110, this force can be transferred onto sealant rear face 144, through sealant 130 and disk 120 and sealant 130 again, through sealant front face 142, and against well base 82. By bearing against well base 82, the sealant 130 of sealant front face 142 can slowly deform plastically to create initial primary seal 150. The force through sealant 130 can also cause sealant 130 to slowly deform to create initial secondary seal 160 between sealant circumferential face 146 and well surface 84. The force through sealant 130 can also cause any residual sealant 130 to flow into device 10.
When device 10 is lowered a sufficient depth into the sea, the hydrostatic pressure of seawater 12 can create sufficient additional force against plunger rear face 114, to again cause sealant 130 to plastically flow and deform. The force through sealant 130 can create, maintain, or enhance primary seal 150 and/or secondary seal 160.
The dimensions of the components of sealwell 80 and seal assembly 100 can be designed and specified to be compatible with the expected dimensions of communications cables 20 and 36, and the expected depth of operation of submarine fiber optic transmission device 10. However, because of the need to form highly reliable seals, it can be important to manufacture each of the components of seal well 80 and seal assembly 100 to a relatively high degree of dimensional accuracy. This importance can include the accuracy of the dimensions of encased disk 140. Notably, the portion of sealant 130 including and beneath sealant front face 142 can be removed to arrive at a reduced and desired sealant thickness between sealant front face 142 and disk front face 122. Likewise, the portion of sealant 130 including and beneath sealant front face 142 can be removed to arrive at a reduced and desired length for seal assembly 100.
FIG. 4 provides a cross-sectional view of seal assembly 100. Referring to FIG. 4, the distance from plunger rear face 114 to initial sealant front face 142xe2x80x2 is illustrated as dimension Axe2x80x2. Likewise, the distance from plunger rear face 114 to reduced sealant front face 142xe2x80x3 is illustrated as dimension Axe2x80x3. The distance from disk front face 122 to initial sealant front face 142xe2x80x2 is illustrated as dimension Bxe2x80x2. Likewise, the distance from disk front face 122 to reduced sealant front face 142xe2x80x3 is illustrated as dimension Bxe2x80x3. Note that initial sealant front face 142xe2x80x2 and dimensions Axe2x80x3 and Bxe2x80x3 are potential positions and dimensions of sealant 130 and are shown for illustrative purposes.
If either dimension Axe2x80x2 or Bxe2x80x2 is under their respective specified value range, seal assembly 100 can be rejected. If either dimension Axe2x80x2 or Bxe2x80x2 is over their respective specified value range, seal assembly 100 can be mounted on a lathe and machined to reduce the thickness of sealant 130 between sealant front face 142 and disk front face 122, thereby reducing dimensions Axe2x80x2 and Bxe2x80x2 to dimensions Axe2x80x3 and Bxe2x80x3, respectively. Then dimensions Axe2x80x3 and Bxe2x80x3 can be measured. Similarly, if either dimension Axe2x80x3 or Bxe2x80x3 is under the value specified, seal assembly 100 can be rejected. If either dimension Axe2x80x3 or Bxe2x80x3 is over the value specified, an operator can again use the lathe to reduce dimensions Axe2x80x3 and Bxe2x80x3. This process of measuring and reducing can be repeated as necessary.
Although dimensions Axe2x80x2 and Axe2x80x3 can be mechanically measured, because disk 120 can be completely surrounded by sealant 130, mechanical methods for measuring dimensions Bxe2x80x2 or Bxe2x80x3 can be destructive of sealant 130. Thus, dimensions Bxe2x80x2 and Bxe2x80x3 have traditionally been measured using x-rays.
FIG. 5 illustrates a cross-section of seal assembly 100 being subject to x-rays 180, that can be emitted by x-ray generator 182. X-rays 180 can pass through sealant 130 rather easily, thereby causing only a faint image on x-ray film 184. However, disk 120 and plunger 110 can block most or all of x-rays 180 from reaching x-ray film 184, thereby causing a heavy image on x-ray film 184. Thus, the resulting images on x-ray film 184 can be mechanically measured to provide approximate measurements of dimensions Axe2x80x2, Axe2x80x3, Bxe2x80x2 and Bxe2x80x3 (not shown in FIG. 5).
To increase the accuracy of these approximate measurements, several x-rays can be taken of seal assembly 100, each from a different angle, and the resulting measurements averaged. FIG. 6 shows an end view of seal assembly 100, and illustrates that the relative position of x-ray generator 182 with respect to seal assembly 100 can be rotated into numerous positions, including positions 182xe2x80x2, 182xe2x80x3, and 182xe2x80x2xe2x80x3, each of which can be separated by approximately 60 degrees. Alternatively, the relative position of seal assembly 100 with respect to x-ray generator 182 can be rotated into similar positions. In either case, x-ray film 184 can be aligned to be perpendicular to the x-rays directed from x-ray generator 182.
However, even upon averaging a series of such x-ray measurements, this process provides limited measurement accuracy. Thus, if greater accuracy is desired, revisions to the process for determining the thickness of the sealant between the sealant front face and the disk front face are needed.
Embodiments of the present invention can provide a method for assuring a thickness of a sealant. The sealant can surround a substrate to define a seal assembly. The method can include ultrasonically measuring a thickness of the sealant between a face of the sealant and a surface of the substrate. The method can also include reducing the thickness of the sealant if the thickness of the sealant is greater than a predetermined value.